In the Severe Asthma Research Program (SARP I), we identified novel reducing-oxidizing (redox) biochemical disorders that characterize severe asthma and defined severe asthma subpopulations based on these abnormalities. There were three major categories of redox abnormalities: (1) impaired regulation of airway acidity, (2) increased oxidation and loss of antioxidant superoxide dismutase (SOD) activity, and (3) alterations of nitric oxide (NO) metabolism with loss of beneficial S-nitrosothiols and formation of cytotoxic reactive nitrogen species. Here, we hypothesize that the pathophysiology of severe asthma is related to abnormalities of enzymes regulating airway redox biochemistry, including CuZnSOD, and two enzymes recently identified to play a role in asthma pathophysiology, arginase and S-nitrosoglutathione reductase (GSNOR). We propose to define how redox abnormalities are interacting determinants of asthma severity and serve as biomarkers for prognosis and evaluation of adequacy of therapy. We will test our hypotheses through three site-specific aims which use the SARP collaborative network and Systemic Triamcinolone in Asthma Characterization (STAC) protocol. In aim 1, we will 1) validate exhaled breath condensate as a tool for measuring airway inflammation-associated acidification;2) investigate mechanisms of airway pH dysregulation;and 3) study the relevance of neutralizing airway pH for treatment and prevention of redox-related damage in severe asthma. In aim 2, we will determine whether or not loss of SOD activity and formation of reactive oxygen species are biomarkers for, and/or determinants of, severe asthma. Mechanisms for loss of activity will be investigated through study of CuZnSOD modifications. In aim 3, we investigate formation of cytotoxic nitrogen oxides and loss of beneficial nitrogen oxides. As the majority of adult severe asthmatics in SARP I were women, we also investigate gender/estrogen effects on severe asthma and NO. Our preliminary data suggest that NO metabolism, particularly GSNOR expression, is influenced by estrogen. The overarching goals of our studies are 1) development of improved asthma monitoring;and 2) design of innovative therapies tailored to specific biochemical abnormalities in severe asthma patients for whom therapeutic options are limited. At the conclusion of this project, we anticipate that we will be able to identify severe asthma redox phenotypes and to begin to develop therapies specific to individual biochemical disturbances.